Power conversion system

ABSTRACT

A capacitor 8 is connected in parallel to both ends of two series-connected semiconductor devices 1, the connecting terminals of the capacitor are arranged so that they become immediately close to the terminal positions of the semiconductor devices 1, inductance of a loop circuit comprising the semiconductor devices 1 and capacitors 8 is suppressed o below 250 nH and thus, a semiconductor switching circuit is constructed. Three sets of this semiconductor switching circuit are connected in parallel with each other, both ends of upper and lower series-connected semiconductor devices in the semiconductor switching circuit are made the main circuit inputs or outputs and the intermediate connecting point of the upper and lower semiconductor devices is made the main circuit output or input and using the capacitors 8 as filter capacitors and surge voltage absorbing capacitors and thus, a power converter is constructed by only two kinds of capacitors and semiconductors.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power conversion system.

2. Description of the Related Art

FIG. 25 shows a circuit diagram of a power conversion system for carslike a converter circuit and an inverter circuit using semiconductorswitching devices, for instance, GTO so far available and a blockdiagram of the system is shown in FIG. 26. A conventional powerconversion system for cars is connected with a snubber circuitcomprising a snubber diode 2, snubber condenser or capacitor 3, and asnubber resistor 4 at both ends of a semiconductor device 1. The snubberdiode 2 and the snubber capacitor 3 are connected in series and bothends of these are connected in parallel to both ends of thesemiconductor device 1. The snubber resistor 4 is connected to thesnubber diode 2 in parallel.

This snubber circuit is for suppressing voltage applied to both ends ofthe semiconductor device 1 when it is switched within its rated voltageand it is needed to reduce the inductance of a looped circuit comprisingthe semiconductor device 1, snubber diode 2 and snubber capacitor 3.Therefore, it becomes necessary to arrange the snubber diode 2 and thesnubber capacitor 3 immediately close to the semiconductor device 1. Thesnubber resistor 4 is provided for the purpose of discharging energyaccumulated in the snubber capacitor 3 and is arranged at a portion (anopening portion) of the system to communicate with the atmospherelikewise cooling fins of a semiconductor cooler 5 in many cases byconsidering heat radiation.

A switching command is output from a gate amplifier 6 and input to thesemiconductor device 1. Further, for the power for a main circuit of apower converter, power of stabilized voltage is supplied from a filtercapacitor 7 connected in parallel to a power converter. The filtercondenser or capacitor 7 is connected to a power source outside thesystem.

In case of a conventional power conversion system for use in railwaycars in the above-mentioned structure, it was needed to arrange twokinds of parts, that is, the snubber diode 2 and the snubber capacitor 3immediately close to the semiconductor device 1 and by bringing theterminal positions of these parts close to each other so as to reduceinductance of connected wires as could as possible. However, in order toarrange two kinds of different parts closely each other, special shapedparts had to adopt and security of reliability and reduction in partcosts using standard shaped parts were difficult and furthermore, thenarrowed spaces between parts impeded the flow of heat generated insidethe system, and a problem of temperature rise in the system wasgenerated. Further, regarding the construction, the system was notrationally assembled and if troubles occurred, the inspection andremoval of parts were difficult.

In addition, as heat to be radiated to the outside of the system, it isnecessary to radiate not only heat generated from the semiconductordevice 1 but also heat generated from the snubber resistor 4 and forinstance, in case of a power conversion system that is installed underthe floor of a railway carriage, the temperature under the floor israised by the exhaust heat from the system and adversely affected thefeeder line under the floor not a little. Therefore, it was so fardemanded to realize a power conversion system that is highly reliable,small in size, light in weight, simple in construction and capable ofsuppressing a price low.

However, in order to realize such a power conversion system with asnubber circuit eliminated, it was necessary to solve technical problemsshown below. In the main circuit for electric car driving, surge voltageVp is generated when large current I of 2300A is cut off even when DCvoltage is 1800V as shown in the chart in FIG. 27. So, for such a powertransistor as GTO that is adopted in an inverter circuit and a convertercircuit as a power conversion system, a power transistor of a lowerrated value that suppresses the peak of surge voltage Vp by absorbingsurge voltage by providing a snubber circuit was so far adopted.

However, in case of such a voltage driving type high-frequency switchingdevice as IGBT (Insulated Gate Bipolar Transistor) or IEGT (InjectionEnhanced Gate Transistor) that is capable of high-speed switching atcontinuous 700 Hz (a conventional GTO is a current driving typeswitching device capable of switching at about continuous 500 Hz), wheninductance of a loop circuit enclosed by conductors connecting aswitching device and a capacitor is reduced by reducing internalinductance of a surge voltage absorbing capacitor and that of conductorsas could as possible, it becomes possible to construct a semiconductorswitching circuit requiring no snubber circuit.

In other words, as shown in FIG. 28, DC voltage for a main circuit foran electric car is generally 1800V and when a semiconductor switchingdevice of rated voltage 3300V is adopted and the system is so set as tosuppress surge voltage Vp generated when breaking the semiconductorswitching circuit by breaking current 2300A to suppress to below 3000Vwith a margin of about 10% against the rated voltage of the switchingdevice, it becomes possible to compose a power converter with less asnubber circuit when an inductance of the loop circuit is suppressed to250 nH or below.

In order to suppress an inductance of the loop circuit to below 250 nH,when a capacitor having an internal low inductance of about 50 nH isadopted and a circuit is in a physical structure to suppress an overallinductance of conductors to below 200 nH, it is possible to realize acircuit satisfying the condition. So, in order to realize such acircuit, it is needed to bring surge voltage absorbing capacitors andsemiconductor switching devices as close as possible and also, bringconductors connecting semiconductor devices each other and conductorsconnecting semiconductor switching devices and capacitors so that anarea enclosing a loop circuit is made small and lengths of conductorsare made short.

SUMMARY OF THE INVENTION

The present invention has been made according to the consideration andit is an object to provide a power conversion system requiring nosnubber circuit that was so far indispensable, with less number of partsand kinds, remarkably improved reliability, small in size and light inweight and capable of achieving low price.

In order to achieve the above-mentioned object, the power conversionsystem according to the invention is characterized in that capacitorsthat serve as capacitors for filtering and absorbing surge voltage areconnected to both ends of series-connected semiconductor devices thatare voltage driven high frequency switching devices in parallel, theconnecting terminals of this capacitors are arranged so that they arebrought immediately close to the terminal positions of the semiconductordevices, more than two sets of semiconductor switching circuits withinductance of which loop circuit comprising the semiconductor devicesand capacitors reduced to below 250 nH are connected in parallel andboth ends and an intermediate connecting point of the series-connectedsemiconductor devices in each semiconductor switching circuits are usedas the main circuit terminals for external connection.

According to the invention, it is possible to construct a main circuitof a power conversion portion by eliminating a snubber circuit that wasadopted so far as a conventional peripheral circuit of semiconductordevice and using only two kinds of components; that is, a closelyarranged capacitor serving as a filter capacitor and surge voltageabsorbing capacitor and the semiconductor device.

When more than two units of the same capacitors in the same capacityconnected in parallel are used as capacitors, inductance can be reducedwhen the capacitors are connected in parallel and a power conversionsystem with a good switching capacity can be constructed.

When the capacitor uses its case as either one of the electrodeterminals of its capacitor, inductance of the capacitor itself can bemade low.

When the capacitor is arranged so that its electrode terminal faces thedirection of the semiconductor devices, inductance at the connectingpoint of the capacitor and the semiconductor devices can be reduced.

When the terminals of the capacitor is arranged immediately close to theintermediate position of the semiconductor devices that are connected inseries, it is possible to reduce inductance at the connecting portion ofthe capacitor and the semiconductor devices.

When the terminals of the capacitor are arrange immediately close toboth end positions of the semiconductor devices that are connected inseries, it is possible to reduce inductance at the connecting portion ofthe capacitor and the semiconductor devices.

Further, a power conversion system according to the invention ischaracterized in that the first capacitor for surge voltage absorbingand the second capacitor as a filter capacitor with the capacity largerthan that of the first capacitor are connected to both ends of theseries-connected semiconductor devices that are voltage driven highfrequency switching devices, the first capacitor is arranged at aposition closer to the semiconductor devices than the second capacitor,more than two sets of semiconductor switching circuits with inductanceof which loop circuit comprising the semiconductor devices and the firstcapacitor is reduced to below 250 nH are connected in parallel, and bothends and intermediate connecting point of the series-connectedsemiconductor devices in each semiconductor switching circuits are usedas the main circuit terminals for the external connection.

According to the invention, as the first capacitor small in size andcapacity than a filter capacitor is provided more immediately close tothe semiconductor devices as a filter capacity for absorbing surgevoltage in addition to the second capacitor, it is possible to constructa semiconductor switching circuit with the inductance of a loopedcircuit comprising the semiconductor devices and the first capacitorreduced to below 250 nH and as a result, it becomes possible toeliminate a conventional snubber circuit and construct a main circuit ofthe power conversion portion only by the semiconductor devices and twokinds of capacitors.

When more than two units of capacitors in the same small capacity areconnected in parallel as the first capacitor, it becomes possible toreduce inductance by connecting capacitors in parallel and construct apower conversion system of good switching characteristic.

When the case of the first capacitor is used as either one of theelectrode terminals of the first capacitor, it is possible to reduceinductance of the capacitor itself.

When the electrode terminals of the first capacitor are arranged to facethe direction of the semiconductor devices, it is possible to reduceinductance at the connecting portion of the first capacitor and thesemiconductor devices.

When as the terminals of the first capacitor are arranged immediatelyclose to the intermediate position of the semiconductor devices that areconnected in series, it is possible to reduce inductance of theconnecting portion of the first capacitor and the semiconductor devices.

When as the terminals of the first capacitor are arranged immediatelyclose to both ends of the semiconductor devices that are connected inseries, it is possible to reduce inductance of the connecting portion ofthe first capacitor and the semiconductor devices.

When the semiconductor devices, the first capacitor and the secondcapacitor are arranged hierarchically, the first capacitor is connectedto both ends of the semiconductor devices that are connected in seriesand the second capacitor is connected to the connecting points, that is,the electrode terminals of the first capacitor, the second capacitorthat is as a filter capacity is connected to the first capacitor side,that serves as a phase capacitor arranged most immediately close to thesemiconductor devices that are connected in series so that the effect bythe switching operation of other phase semiconductor device iseliminated and the shape of conductors for connecting between thecapacitors and the semiconductor devices can be simplified.

When the number of the second capacitors is reduced less than the numberof sets of the semiconductor switching circuits that are connected inparallel and more than two sets of the semiconductor switching circuitsconnected in parallel are connected commonly to at least one unit of thesecond capacitor, it is possible to reduce the number of parts byintegrating the second capacitors that serve as filter capacitorswithout providing it for each phase.

When the second capacitor is constructed as a filter capacitor that hasa required capacity using a main capacitor in the main circuit unitincluding semiconductor devices and an auxiliary capacitor installed atthe outside of the main circuit unit and therefore, it is possible toconstruct a filter capacitor that has a proper capacity corresponding toa system by using a capacitor of a proper capacity as an auxiliarycapacitor outside the main circuit unit and the main circuit can bestandardized.

Further, a power conversion system according to the invention ischaracterized in that including more than two sets of semiconductorswitching circuits connected in parallel comprising surge voltageabsorbing capacitor connected in parallel to both ends ofseries-connected semiconductor devices that are voltage drivenhigh-frequency switching devices and both ends and the intermediateconnecting point of the series-connected semiconductor devices in thesemiconductor switching circuits are made the main circuit terminal forexternal connection, wherein

the semiconductor devices are press fit shape semiconductor devices ofwhich both surfaces serve as the electrode surfaces,

the positive pole sides or the negative pole sides of each semiconductordevices of an upper arm side and a lower arm side in theseries-connected semiconductor devices of the semiconductor switchingcircuits are press fitted by way of an insulating plate having largethermal conductivity on the same plane of semiconductor device cooler,and

the negative poles of the upper arm side semiconductor devices and thepositive poles of the lower arm side semiconductor devices are connectedby conductors and the positive poles of the upper arm side semiconductordevices and the negative poles of the lower arm side semiconductordevices are connected by one set of conductors which are close to bothsides of the capacitors.

Further, a power conversion system according to the invention ischaracterized in that including more than two sets of semiconductorswitching circuits connected in parallel comprising surge voltageabsorbing capacitors connected in parallel to both ends ofseries-connected semiconductor devices that are voltage drivenhigh-frequency switching devices and both ends and the intermediateconnecting point of the series-connected semiconductor devices in thesemiconductor switching circuits are made the main circuit terminal forexternal connection, wherein

the semiconductor devices are press fit shape semiconductor devices ofwhich both surfaces serve as the electrode surfaces,

the negative pole side of the upper arm side semiconductor device andthe positive side of the lower arm side semiconductor device of theseries-connected semiconductor devices of the semiconductor switchingcircuits are press fitted on the same plane of the semiconductor devicecooler of good conductivity, and

the positive pole of the upper arm side semiconductor device and thenegative pole of the lower arm side semiconductor device are connectedrespectively by one set of conductors that are close to both terminalsof the capacitors.

Further, a power conversion system according to the invention ischaracterized in that including more than two sets of semiconductorswitching circuits connected in parallel comprising surge voltageabsorbing capacitors connected in parallel to both ends ofseries-connected semiconductor devices that are voltage drivenhigh-frequency switching devices and both ends and the intermediateconnecting point of the series-connected semiconductor devices in thesemiconductor switching circuits as the main circuit terminals forexternal connection, wherein

the semiconductor devices are press fit shape semiconductor devices ofwhich both surfaces serve as the electrode surfaces,

the negative pole side of the upper arm side semiconductor device andthe positive pole side of the lower arm side semiconductor devices ofthe series-connected semiconductor devices of the semiconductorswitching circuits are press fitted on the same plane of thesemiconductor device cooler with a common conductor put between them,and

the positive pole of the upper arm side semiconductor device and thenegative pole of the lower arm side semiconductor device are connectedrespectively by one set of conductors that are close to both terminalsof the capacitors.

Further, a power conversion system according to the invention ischaracterized in that including more than two sets of semiconductorswitching circuits connected in parallel comprising surge voltageabsorbing capacitors connected in parallel to both ends ofseries-connected semiconductor devices that are voltage drivenhigh-frequency switching devices and both ends and the intermediateconnecting point of the series-connected semiconductor devices in thesemiconductor switching circuits as the main circuit terminals forexternal connection, wherein

the semiconductor devices are press fitted shape semiconductor devicesof which both surfaces serve as the electrode surfaces,

the positive pole sides of the upper arm side semiconductor devices andthe negative pole sides of the lower arm side semiconductor devices ofthe series-connected semiconductor devices of the semiconductorswitching circuits are press fitted on the same plane of thesemiconductor device cooler by way of an insulating plate of largethermal conductivity, and

the negative pole sides of the upper arm side semiconductor devices andthe positive pole sides of the lower arm side semiconductor devices areconnected by conductors, and the positive pole of the upper arm sidesemiconductor device and the negative pole of the lower arm sidesemiconductor device are connected respectively by one set of conductorsthat are close to both terminals of the capacitors.

According to the above mentioned inventions, using press fit statesemiconductor of which both sides become the electrode surfaces, eachswitching circuit is constricted by assembling the semiconductor devicesand conductors hierarchically to the cooler and fixed by compressing theentirety from the outside, the semiconductor devices and capacitors canbe closely arranged in each semiconductor switching circuit, inductanceof a loop circuit comprising semiconductor devices, capacitors andconductors can be suppressed to below 250 nH, and it is possible toeliminate a snubber circuit and construct a power conversion portiononly by two kinds of circuit components of capacitors and semiconductordevices.

Further, a power conversion system according to the invention ischaracterized in that including more than two sets of semiconductorswitching circuits connected in parallel comprising surge voltageabsorbing capacitors connected in parallel to both ends ofseries-connected semiconductor devices that are voltage drivenhigh-frequency switching devices and both ends and the intermediateconnecting point of the series-connected semiconductor devices in thesemiconductor switching circuits as the main circuit terminals forexternal connection, wherein

the semiconductor devices are modular type semiconductor devicesprovided with the positive pole terminals and the negative poleterminals on one of the surfaces and the opposite surfaces are flatcooling and mounting surfaces,

the series-connected semiconductor devices of the semiconductorswitching circuits are mounted on the same plane of the semiconductordevice coolers with the negative terminal sides of the upper arm sidesemiconductor devices and the positive pole sides of the lower arm sidesemiconductor devices arranged in parallel with and adjoining each otherin the same directions, and

the negative pole sides of the upper arm side semiconductor devices andthe positive pole sides of the lower arm side semiconductor devices areconnected by conductors, and the positive pole of the upper arm sidesemiconductor device and the negative pole of the lower arm sidesemiconductor device are connected respectively by one set of conductorsthat are close to both terminals of the capacitors.

Further, a power conversion system according to the invention ischaracterized in that including more than two sets of semiconductorswitching circuits connected in parallel comprising surge voltageabsorbing capacitors connected in parallel to both ends ofseries-connected semiconductor devices that are voltage drivenhigh-frequency switching devices and both ends and the intermediateconnecting point of the series-connected semiconductor devices in thesemiconductor switching circuits as the main circuit terminals forexternal connection, wherein

the semiconductor devices are modular type semiconductor devicesprovided with the positive pole terminals and the negative poleterminals on one of the surfaces and the opposite surfaces are flatcooling and mounting surfaces,

the series-connected semiconductor devices of the semiconductorswitching circuits are mounted on the same plane of the semiconductordevice coolers in the arrangement so that the line connecting thepositive pole terminals and the negative pole terminals of the upper armside semiconductor devices becomes in parallel with the line connectingthe positive pole terminal and the negative pole terminal of the lowerside arm semiconductor devices and the positive and negative directionsbecome opposite each other, and

the negative pole sides of the upper arm side semiconductor devices andthe positive pole sides of the lower arm side semiconductor devices areconnected by conductors, and the positive pole of the upper arm sidesemiconductor device and the negative pole of the lower arm sidesemiconductor device are connected respectively by one set of conductorsthat are close to both terminals of the capacitors.

According to the above mentioned inventions as each semiconductorswitching circuit is constructed using modular semiconductor deviceswith the positive and negative pole terminals provided on one of thesurfaces and the other surface becomes the flat cooling and mountingsurface and semiconductor devices are horizontally arranged and thecooler is mounted on the mounting surface side and between the positiveand negative pole terminals on the opposite surface and the terminalsand capacitors are connected by conductors, the semiconductor devicesand the capacitors can be arranged closely in each semiconductorswitching circuit, inductance of a loop circuit comprising semiconductordevices, capacitors and conductors can be suppressed to below 250 nH,and it is possible to eliminate a snubber circuit and construct a maincircuit of a power conversion portion only by only two kinds of circuitcomponents; capacitors and semiconductor devices.

When semiconductor devices are brought in contact with separatesemiconductor device coolers, it is possible to cool semiconductordevices individually without subject to the heat generation of othersemiconductor devices and further, it is also possible to prepare acooler provided with a cooling capability corresponding to the heatgenerating state of each semiconductor device, thus improving thecooling effect of the semiconductor devices.

When the radiation capacity of the semiconductor device cooler providedat the downstream side of the flow of air warmed by the heat radiationof the semiconductor cooler is made higher than that of thesemiconductor device cooler at the upper stream side, it is possible tobalance the temperature rise of each cooler and effectively cool thesemiconductor devices.

When the series-connected semiconductor devices are brought in contactwith the same semiconductor device cooler in the state shifted to theupper stream side of the air warmed by the heat radiated from thatsemiconductor device cooler, the temperature rises at various parts ofthe cooler are made uniform and the semiconductor devices can beeffectively cooled.

Further, a power conversion system according to the invention ischaracterized in that including more than two sets of semiconductorswitching circuits connected in parallel comprising surge voltageabsorbing capacitors connected in parallel to both ends ofseries-connected semiconductor devices that are voltage drivenhigh-frequency switching devices and both ends and the intermediateconnecting point of the series-connected semiconductor devices in thesemiconductor switching circuits as the main circuit terminals forexternal connection, wherein

the semiconductor devices are press fit semiconductor devices of whichboth surfaces serve as the electrode surfaces,

the negative pole side of the upper arm side semiconductor device andthe positive pole side of the lower arm side semiconductor device of theseries-connected semiconductor devices of the semiconductor switchingcircuit are press fitted to the front and back of the heat collectingblock portion of the semiconductor device cooler having a flat and goodconductive heat collecting block portion and a radiating portion toradiate the heat collected by this heat collecting block portion,respectively,

the positive pole of the upper arm side semiconductor device and thenegative pole of the lower arm side semiconductor device are connectedby one set of conductors that are close to both terminals of thecapacitor, respectively.

According to the invention, as press fit type semiconductor devices ofwhich both surfaces become the electrode surfaces are used assemiconductor devices, coolers that have a flat and good conductive heatcollecting block portion and a heat radiating portion to radiate heatcollected by the heat collecting block portion are used as coolers, thesemiconductor devices and conductors are assembled to this cooler heatcollecting block portion in the laminated structure and thesemiconductor switching circuits are constructed by compressing andfixed the entirety from the outside, the semiconductor devices andcapacitors are arranged closely in each semiconductor switching circuit,inductance of a loop circuit comprising the semiconductor devices,capacitors and conductors can be suppressed to below 250 nH and it ispossible to eliminate a snubber circuit and construct the main circuitof the power conversion portion only by two circuit components;capacitors and semiconductor devices. Furthermore, as the goodconductive heat collecting block portion of the cooler serves is alsoused for connecting for the semiconductor devices, it becomes possibleto make the intermediate connecting portion between the upper and lowerarm semiconductor devices most short, simplify the construction andreduce inductance of the loop circuit.

Further, a power conversion system according to the invention ischaracterized in that including more than two sets of semiconductorswitching circuits connected in parallel comprising surge voltageabsorbing capacitors connected in parallel to both ends ofseries-connected semiconductor devices that are voltage drivenhigh-frequency switching devices and both ends and the intermediateconnecting point of the series-connected semiconductor devices in thesemiconductor switching circuits as the main circuit terminals forexternal connection, wherein

the semiconductor devices are press fit semiconductor devices of whichboth surfaces serve as the electrode surfaces,

the negative pole side of the upper arm side semiconductor device andthe positive pole side of the lower arm side semiconductor device of theseries-connected semiconductor devices of the semiconductor switchingcircuit are press fitted to the front and back of the heat collectingblock portion of the semiconductor device cooler having a flat and goodconductive heat collecting block portion and a radiating portion toradiate the heat collected by this heat collecting block portion,respectively,

the heat collecting block portions of separate two semiconductor devicecoolers that have flat good conductive heat collecting block portionsand radiating portions to radiate the heat collected by this heatcollecting block portions are press fit to the positive pole side of theupper arm side semiconductor device and the negative pole side of thelower arm side semiconductor device, respectively, and

the heat collecting block portion of the separate semiconductor devicecooler to which the positive pole side of the upper arm sidesemiconductor device is press fitted and the heat collecting bockportion of the separate semiconductor device cooler to which thenegative pole side of the lower arm side semiconductor device is pressfitted are connected to both terminals of the capacitor by one set ofconductors that are close to each other.

According to the invention, as press fit type semiconductor devices ofwhich both surfaces become the electrode surfaces are used assemiconductor devices, coolers that have a flat and good conductive heatcollecting block portion and a heat radiating portion to radiate heatcollected by the heat collecting block portion are used as coolers, thesemiconductor devices and conductors are assembled to this cooler heatcollecting block portion in the laminated structure and further, a heatcollecting block portion of a separate cooler is assembled to theoutside of the upper and lower semiconductor devices separately in thelaminated structure and the semiconductor switching circuits areconstructed by compressing and fixing the entirety from the outside, thesemiconductor devices and capacitors are arranged closely in eachsemiconductor switching circuit, inductance of a loop circuit comprisingthe semiconductor devices, capacitors and conductors can be suppressedto below 250 and it is possible to eliminate a snubber circuit andconstruct the main circuit of the power conversion portion only by twokinds of circuit components; capacitors and semiconductor devices.Furthermore, the power conversion system becomes such a construction toclamp the upper and lower arm semiconductor devices of eachsemiconductor switching circuit by the heat collecting block portions ofthe coolers from the front and back surfaces and it is thereforepossible to increase the cooling effect of the semiconductor devices.

Further, a power conversion system according to the invention ischaracterized in that including more than two sets of semiconductorswitching circuits connected in parallel comprising surge voltageabsorbing capacitors connected in parallel to both ends ofseries-connected semiconductor devices that are voltage drivenhigh-frequency switching devices and both ends and the intermediateconnecting point of the series-connected semiconductor devices in thesemiconductor switching circuits as the main circuit terminals forexternal connection, wherein

the semiconductor devices are press fit semiconductor devices of whichboth surfaces serve as the electrode surfaces,

the same positive pole surface sides or the negative pole surface sidesof the series-connected semiconductor devices of the semiconductorswitching circuits are press fitted to the front and back of the heatcollecting block portion of the semiconductor device cooler having theflat heat collecting block portion and the radiating portion to radiatethe heat collected by this heat collecting block portion by way ofelectric insulating plate having large thermal conductivity,respectively,

the negative pole side of the upper arm side semiconductor device andthe positive pole side of the lower arm side semiconductor device of theseries-connected semiconductor devices are connected by conductors, and

the positive pole of the upper arm side semiconductor device and thenegative pole of the lower arm side semiconductor device are connectedto both terminals of the capacitor by one set of conductors that areclose to each other.

According to the invention, as press fit type semiconductor devices ofwhich both surfaces become the electrode surfaces are used assemiconductor devices, coolers that have a flat heat collecting blockportion and a heat radiating portion to radiate heat collected by theheat collecting block portion are used as coolers, the semiconductordevices and conductors are assembled to this cooler heat collectingblock portion in the laminated structure via an insulating plate havinga large thermal conductivity and the semiconductor switching circuitsare constructed by compressing and fixing the entirety from the outside,and therefore, the semiconductor devices and capacitors can be arrangedclosely in each semiconductor switching circuit, and inductance of theloop-shape circuit comprising the semiconductor devices, capacitors andconductors can be suppressed to below 250 nH and it is possible toeliminate a snubber circuit and construct the main circuit of the powerconversion portion by only two kinds of circuit components; capacitorsand semiconductor devices. Furthermore, as the semiconductor devices andconductors are press fitted to the heat collecting block portion of thecooler via an insulating plate, it is possible to cool the semiconductordevices effectively and insulate the cooler.

Further, a power conversion system according to the invention ischaracterized in that including more than two sets of semiconductorswitching circuits connected in parallel comprising surge voltageabsorbing capacitors connected in parallel to both ends ofseries-connected semiconductor devices that are voltage drivenhigh-frequency switching devices and both ends and the intermediateconnecting point of the series-connected semiconductor devices in thesemiconductor switching circuits as the main circuit terminals forexternal connection, wherein

the semiconductor devices are press fit semiconductor devices of whichboth surfaces serve as the electrode surfaces,

the same positive pole surface sides or the negative pole surface sidesof the series-connected semiconductor devices of the semiconductorswitching circuits are press fitted to the front and back of the heatcollecting block portion of the semiconductor device cooler having theflat heat collecting block portion and the radiating portion to radiatethe heat collected by this heat collecting block portion by way ofelectric insulating plate having large thermal conductivity,respectively,

the heat collecting block portions of separate two semiconductor devicecoolers that have flat heat collecting block portions and radiatingportions to radiate the heat collected by this heat collecting blockportions are press fit to the electrode surface positioned at theoutside of the upper arm side semiconductor device and the electrodeside positioned at the outside of the lower arm side semiconductordevice, respectively by way of an insulating plate having large thermalconductivity,

the negative pole side of the upper arm side semiconductor device andthe positive pole side of the lower arm side semiconductor device of theseries-connected semiconductor devices are connected by conductor, and

the positive pole of the upper arm side semiconductor device and thenegative pole of the lower arm side semiconductor device are connectedto both terminals of the capacitor by one set of conductors that areclose to each other.

According to the above invention, as press fit type semiconductordevices of which both surfaces become the electrode surfaces are used assemiconductor devices, coolers that have a flat heat collecting blockportion and a heat radiating portion to radiate heat collected by theheat collecting block portion are used as coolers, the semiconductordevices and conductors are assembled to this cooler heat collectingblock portion in the laminated structure via an insulating plate havinga large thermal conductivity and the semiconductor switching circuitsare constructed by compressing and fixing the entirety from the outside,and therefore, the semiconductor devices and capacitors can be arrangedclosely in each semiconductor switching circuit, and inductance of theloop-shape circuit comprising the semiconductor devices, capacitors andconductors can be suppressed to below 250 nH and it is possible toeliminate a snubber circuit and construct the main circuit of the powerconversion portion by only two kinds of circuit components; capacitorsand semiconductor devices. Furthermore, as the power conversion systembecomes such structure to clamp the upper and lower arm semiconductordevices of the semiconductor switching circuits by the heat collectingblock portion of the cooler from the front and back surfaces, it ispossible to increase the cooling effect of the semiconductor devices.

Further, a power conversion system according to the invention ischaracterized in that including more than two sets of semiconductorswitching circuits connected in parallel comprising surge voltageabsorbing capacitors connected in parallel to both ends ofseries-connected semiconductor devices that are voltage drivenhigh-frequency switching devices and both ends and the intermediateconnecting point of the series-connected semiconductor devices in thesemiconductor switching circuits as the main circuit terminals forexternal connection, wherein

the semiconductor device is modular type semiconductor device providedwith the positive and negative terminals on one of its surfaces and theopposite surface is a flat cooling and mounting surface,

the series-connected semiconductor devices of the semiconductorswitching circuits are so arranged that the mount surfaces face eachother and the negative pole terminal of one of the semiconductor devicesis positioned on the back side of the positive pole terminal of theother semiconductor device,

the mounting surface sides of the series-connected semiconductor devicesof the semiconductor switching circuits are mounted on the front andback sides of the heat collecting block portions of the semiconductordevice cooler that has a flat heat collecting block portion and aradiating portion to radiate the heat collected by this heat collectingblock portion, respectively,

the negative pole terminal of the upper arm side semiconductor deviceand the positive pole terminal of the lower arm side semiconductordevice of the series-connected semiconductor devices are connected by aconductor, and

the positive pole terminal of the upper arm side semiconductor deviceand the negative pole terminal of the lower arm side semiconductordevice are connected to both terminals of the capacitor by one set ofconductors that are close to each other.

According to the invention, as a modular type semiconductor device withthe positive and negative pole terminals provided on one surface and theother surface is a flat cooling and mounting surface is used, a coolerthat has a flat heat collecting block portion and a radiating portion toradiate the heat collected by this heat collecting block portion isused, the mounting surface side of a semiconductor device is mounted tothe front and back of the heat collecting block portion of this cooler,the negative pole terminal of the upper arm side semiconductor deviceand the positive pole terminal of the lower arm side semiconductordevice are connected by a conductor, the positive pole terminal of theupper arm side semiconductor device and the negative pole terminal ofthe lower arm side semiconductor are connected by one set of conductorsthat are close to both terminal of the capacitor and thus, eachsemiconductor switching circuit is constructed, the semiconductordevices and the capacitor are arranged closely, inductance of the loopcircuit comprising the semiconductor devices, the capacitor andconductors can be suppressed to below 250 nH and it becomes possible toeliminate a snubber circuit and construct the main circuit of the powerconversion portion by only two kinds of circuit components; thecapacitor and semiconductor devices.

Further, a power conversion system according to the invention ischaracterized in that including more than two sets of semiconductorswitching circuits connected in parallel comprising surge voltageabsorbing capacitors connected in parallel to both ends ofseries-connected semiconductor devices that are voltage drivenhigh-frequency switching devices and both ends and the intermediateconnecting point of the series-connected semiconductor devices in thesemiconductor switching circuits as the main circuit terminals forexternal connection, wherein

the semiconductor device is a modular type semiconductor device providedwith the positive and negative terminals on one of its surfaces and theopposite surface is a flat cooling and mounting surface,

the series-connected semiconductor devices of the semiconductorswitching circuits are so arranged that the mounting surfaces come tothe outside and the positive pole terminal and negative pole terminalface each other,

the heat collecting block portions of semiconductor device coolers thathave a flat heat collecting block portion and a radiating portion toradiate the heat collected by this heat collecting block portion aremounted on the mounting surfaces of the series-connected semiconductordevices,

the negative pole terminal of the upper arm side semiconductor deviceand the positive pole terminal of the lower arm side semiconductordevice of the series-connected semiconductor devices are connected by aconductor, and

the positive pole terminal of the upper arm side semiconductor deviceand the negative pole terminal of the lower arm side semiconductordevice are connected to both terminal of the capacitor, respectively byone set of conductors that are close to each other.

According to the above invention, as a modular type semiconductor devicewith the positive and negative pole terminals provided on one surfaceand the other surface is a flat cooling and mounting surface is used, acooler that has a flat heat collecting block portion and a radiatingportion to radiate the heat collected by this heat collecting blockportion is used, the semiconductor devices are arranged so that thepositive pole terminal and the negative pole terminal face each other, aheat collecting block portion of the cooler is separately mounted to themounting surface at the outside of the these semiconductor devices, thenegative pole terminal of the upper arm side semiconductor device andthe positive pole terminal of the lower arm side semiconductor deviceare connected by conductor and further, the positive pole terminal ofthe upper arm side semiconductor device and the negative pole terminalof the lower arm side semiconductor device are connected to bothterminal of the capacitor, respectively by one set of conductors thatare close to each other and thus, a semiconductor switching circuit isconstructed, it is therefore possible to arrange the semiconductordevices and the capacitor closely in each semiconductor switchingcircuit and suppress inductance of the looped-shape circuit comprisingthe semiconductor devices, the capacitor and the conductors to below 250nH, eliminate a snubber circuit and construct the main circuit of thepower conversion portion by one two kinds of circuit components; thecapacitor and semiconductor. Furthermore, it is also possible toincrease the cooling effect as the semiconductor devices are mounted toindividual heat collecting block portion.

When a conductor is connected to one of the filter capacitors that alsoserves for surge voltage absorbing, a circuit can be constructed only byone kind of capacitor and the number of parts can be sharply reduced.

When a conductor is connected to the first capacitor in a circuitprovided with 2 kinds of capacitors; the first capacitor for surgevoltage absorbing and the second capacitor as a filter capacitor, it ispossible to adopt a capacitor of small size and small capacity withsmall internal inductance for this first capacitor and it becomespossible to reduce inductance of the looped circuit comprisingsemiconductor devices, capacitors and conductors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a semiconductor switching circuit in thefirst embodiment of the present invention;

FIG. 2 is a block diagram showing the arrangement of parts in theabove-mentioned embodiment;

FIG. 3 is a circuit diagram of a semiconductor switching circuit in thesecond embodiment of the present invention;

FIG. 4 is a block diagram showing the arrangement of parts in theabove-mentioned embodiment;

FIG. 5 is a block diagram showing the arrangement of parts of a powerconversion system in the third embodiment of the present invention;

FIG. 6 is a block diagram showing the arrangement of parts of a powerconversion system in the fourth embodiment of the present invention;

FIG. 7 is a block diagram showing the arrangement of parts of a powerconversion system in the fifth embodiment of the present invention;

FIG. 8 is a side view showing the construction of a power conversionsystem in the sixth embodiment of the present invention;

FIG. 9 is a perspective view showing the construction of the powerconversion system in the above-mentioned embodiment;

FIG. 10 is a side view showing the construction of a power conversionsystem in the seventh embodiment of the present invention;

FIG. 11 is a side view showing the construction of a power conversionsystem in the eighth embodiment of the present invention;

FIG. 12 is a side view showing the construction of a power conversionsystem in the ninth embodiment of the present invention;

FIG. 13 is a perspective view showing an inverter circuit assembledusing the power conversion system in the above-mentioned embodiment;

FIG. 14 is a perspective view showing the construction of a powerconversion system in the tenth embodiment of the present invention;

FIG. 15 is a side view showing the construction of a power conversionsystem in the eleventh embodiment of the present invention;

FIG. 16 is a side view showing the construction of a power conversionsystem in the twelfth embodiment of the present invention;

FIG. 17 is a side view showing the construction of a power conversionsystem in the thirteenth embodiment of the present invention;

FIG. 18 is a side view showing the construction of a power conversionsystem in the fourteenth embodiment of the present invention;

FIG. 19 is a side view showing the construction of a power conversionsystem in the fifteenth embodiment of the present invention;

FIG. 20 is a side view showing the construction of a power conversionsystem in the sixteenth embodiment of the present invention;

FIG. 21 is a side view showing the construction of a power conversionsystem in the seventeenth embodiment of the present invention;

FIG. 22 is a side view showing the construction of a power conversionsystem in the eighteenth embodiment of the present invention;

FIG. 23 is a perspective view showing the construction of a powerconversion system in the nineteenth embodiment of the present invention;

FIG. 24 is a side view showing the construction of a power conversionsystem in the twentieth embodiment of the present invention;

FIG. 25 is a circuit diagram of a semiconductor switching circuit in aconventional example.

FIG. 26 is a block diagram showing the arrangement of parts of asemiconductor switching circuit in a conventional example;

FIG. 27 is a time chart showing the breaking characteristic of asemiconductor switching circuit;

FIG. 28 is a graph showing the relationship between inductance and surgevoltage of a loop circuit of a semiconductor switching circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the attached drawings.

First Embodiment

A circuit diagram of one set of semiconductor switching circuits thatare adopted in the power conversion system in the first embodiment isshown in FIG. 1 and its block diagram is shown in FIG. 2. A condenser ora capacitor 8 is connected to both ends of two series-connectedsemiconductor devices 1 which are voltage driving high-frequencyswitching devices (rated voltage: above 1.2 kV) such as IGBT and IEGT,and semiconductors 1 and capacitor 8 are connected by conductors 9a, 9b,9c. A loop circuit is composed by these conductors 9a, 9b, 9c closelypositioned each other so as to suppress its inductance to below 250 nH.

Here, a capacitor having a low inductance and the same capacity as aconventional filter capacitor 7 is used as the capacitor 8. Thecapacitor 8 is connected to an external power source by conductors 10a,10b and a gate amplifier 6 is connected to the semiconductors 1 to inputa switching command.

One of the electrodes of the capacitor 8 uses a terminal and the otherelectrode uses a case and these electrodes are arranged close to anintermediate connecting point of two series-connected semiconductordevices 1. Further, both electrodes of the capacitor 8 may be arrangedclose to both ends of two series-connected semiconductor devices 1,respectively (This arrangement is also applicable in the embodimentsshown below. Refer to, for instance, the structures shown in FIG. 19 andFIG. 20.)

By providing two or three sets or multiple sets of two or three sets ofthe semiconductor switching circuits in the structure in parallel, andmaking an intermediate connecting point side of two series-connectedsemiconductor devices 1 as the main circuit input point and both ends ofthe semiconductor devices 1 as the main circuit output points, aconverter circuit for converting AC input into DC output is constructed.In this converter circuit, AC input is converted into DC output byinputting a switching command from the gate amplifier 6 to respectivesemiconductor switching circuit so that each semiconductor deviceperforms the switching operation.

On the contrary, by providing 3 sets or multiple sets of 3 sets of thesemiconductor switching circuits in parallel, and making both ends oftwo series-connected semiconductor devices as the main circuit inputpoints and the intermediate connecting point side of the semiconductordevices as the main circuit output point, an inverter circuit to convertDC input into AC output is constructed. In this inverter circuit, DCinput is converted into AC output by inputting a switching command fromthe gate amplifier 6 to respective semiconductor switching circuit sothat each semiconductor device 1 performs the switching operation.

In this case, the inductance of a loop circuit between the capacitor 8and semiconductor devices 1 is reduced to below 250 nH by adopting acapacitor having a low internal inductance below 50 nH for the capacitor8, bringing the capacitor 8 and the semiconductor devices 1 close eachother as could as possible and at the same time, a inductance ofconductors is reduced to below 200 nH by making the lengths of theconductors 9a, 9b, 9c short and bringing them close as could aspossible. As a result, it becomes possible to suppress the surge voltageapplied to both ends of the semiconductor devices 1 within the ratedvoltage of the semiconductor devices, prevent the semiconductor devices1 from being broken by over voltage and assure the satisfactoryswitching operation. Further, as the capacitor 8 uses a capacitor in thesame capacity as the filter capacitor 7 in a conventional system, thecapacitor 8 also serves as a filter capacitor to stable feed supplyvoltage and therefore, the circuit structure becomes simple withoutrequiring a filter capacitor separately.

According to the power conversion system in the first embodiment, asnubber circuit that is a protective circuit around the semiconductordevices can be eliminated and the number of component parts and kinds asa power conversion system can be sharply reduced when compared with aconventional system. Further, as there is no snubber resistor, heat losscan be reduced and coupled with reduced in the number of component partsand simplified structure, the downsized, light weighted and low pricedsystem can be realized.

Second Embodiment

A circuit diagram of one set of semiconductor switching circuits adoptedin the power conversion system in the second embodiment of the presentinvention is shown in FIG. 3 and its block diagram is shown in FIG. 4. Afirst capacitor 11 for surge voltage absorbing and a second capacitor 12as a filter capacitor are connected in parallel to both ends of twoseries-connected semiconductor devices 1. At the side close to thesemiconductor devices 1, the first capacitor 11 is arranged and at theside far away from the semiconductor devices 1, the second capacitor 12is arranged.

The second capacitor 12 uses a capacitor in the same capacity (about1000 μF) as the filter capacitor 7 in a conventional system. Further,the capacity of the first capacitor 11 is below the capacity of thesecond capacitor 12, preferably about 1/10 (about 100 μF) of the secondcapacitor 12, downsized and also, using its capacitor case as one of theelectrodes, its internal inductance is reduced to about 50 nH.

The first capacitor 11 and the semiconductor devices 1 are connected byconductors 9a, 9d, 9e. The conductors 9a, 9d, 9e are made short as couldas possible and brought close each other so as to suppress the overallinductance to below 200 nH so that the inductance of this loop circuitbecomes below 250 nH.

Further, as described above, it is possible to arrange both electrodesof the first capacitor 11 close to the intermediate connecting point oftwo series-connected semiconductor devices 1 and also, to arrange bothelectrodes of the first capacitor 11 close to both ends of twoseries-connected semiconductor devices 1 (these arrangements are alsoapplicable to the embodiments shown below. Refer to, for instance, thestructures shown in FIG. 19 and FIG. 20.)

The second capacitor 12 is arranged at the side farther away from thesemiconductor devices 1 than the first capacitor 11 and the secondcapacitor 12 and the first capacitor 11 are connected by conductors 10c,10d. The semiconductor devices 1, the first capacitor 11 and the secondcapacitor 12 are arranged hierarchically from a cooler 5 so as to makemutual connection of conductors easy. Further, two series-connectedsemiconductor devices 1 are arranged in parallel close to the cooler 5as that the length of the conductor 9a between two semiconductor devices1 becomes most short.

Two or three or multiple sets of semiconductor switching circuits in theconstruction are connected in parallel so as to construct a convertercircuit or an inverter circuit likewise the first embodiment, and aswitching command is input to respective semiconductor circuits from thegate amplifier 6 so that the semiconductor devices 1 make the switchingoperation to convert AC input to DC output (in case of the convertercircuit) or DC power into AC output (in case of the inverter circuit).

In this case, likewise the first embodiment, as inductance of a loopcircuit that is enclosed by the first capacitor 11 and the semiconductordevices 1 is 250 nH or below, surge voltage applied to both ends of thesemiconductor devices 1 can be suppressed within the range of the ratedvoltage of the semiconductor device and the satisfactory switchingoperation can be made without breaking the system. Further, the secondcapacitor 12 uses a capacitor in the same capacity as the filtercapacitor in a conventional system and serves as a filter capacity tostably feed supply voltage.

According to the power conversion system in the second embodiment, asthe first capacitor 11 for surge voltage absorbing was separated fromthe second capacitor 12 that is a filter capacitor, there are suchmerits that it becomes possible to make the system in more small sizeand arrange it close to the semiconductor devices 1 and reduceinductance when installed. Further, as a snubber circuit that is aprotective circuit around the semiconductor devices was eliminated, itbecomes possible to reduce the number of parts and kinds sharply. Inaddition, as a snubber resistor was eliminated, heat loss can be reducedand coupled with reduction of the number of parts, simplifiedconstruction, it becomes possible to achieve the downsized lightweighted and low priced system.

Third Embodiment

The construction of the power conversion system in the third embodimentof the present invention is shown in FIG. 5. The power conversion systemin the third embodiment is an inverter circuit that is composed of 3sets of the semiconductor device adopted in the second embodiment shownin FIG. 3 and FIG. 4 arranged in parallel. However, although it ispossible to construct an inverter circuit by arranging 3 sets of thesemiconductor switching circuit adopted in the second embodiment, inthis power conversion system in the third embodiment, two units of thesecond capacitor 12a are provided for 3 sets of the semiconductorswitching circuit.

The operation of this power conversion system in the third embodiment isthe same as that of the power conversion system in the secondembodiment. However, as the number of units of the second capacity 12ais reduced, the more number of parts and the price can be reducedaccordingly.

Further, it is also possible to reduce the number of units of the secondcapacitor 12a to only one unit and in this case, there is such a meritthat the configuration of conductors to connect the second capacitor tothe first capacitor 11 can be more simplified.

Fourth Embodiment

The construction of the power conversion system in the fourth embodimentof the present invention is shown in FIG. 6. The arrangement of thefirst capacitor 11 and the second capacitor 12a is the same as that ofthe power conversion system in the third embodiment. However, regardingthe connections of capacitors by conductors in this fourth embodiment,two units of the second capacitors 12a are connected to the firstcapacitor 11 at the central position of three phases by conductors 10g,10h, 10i, 10j and the second capacitor 12a only arranged at the sideclose to the first capacitor is connected to each of the firstcapacitors 11 arranged at both sides of three phases by conductors.

Further, in the power conversion system of the fourth embodiment, inaddition to the second capacitors 12a that become the main elements ofthe filter capacitors provided in the main circuit unit, a thirdcapacitor 13 that becomes an auxiliary element of the filter capacitorsis arranged at the outside of the main circuit unit and connected to themain circuit unit by conductors 10k, 101.

The filter capacitor is thus constructed by the second capacitors 12a inthe main circuit unit and the external third capacitor 13, and when thecapacity of the external third capacitor 13 is selected, it is possibleto correspond the capacity of the filter capacitor to a filter constantrequired for the system without change a capacity constant of thecapacitor of the main circuit and the main circuit unit can be madecommonly usable.

Fifth Embodiment

The construction of the power conversion system in the fifth embodimentof the present invention is shown in FIG. 7. In this power conversionsystem in the fifth embodiment, two units of the first capacitor 11a areconnected in parallel to one phase of a semiconductor switching circuitcomprising two series-connected semiconductor device 1. Further, thefirst capacitor 11a keeps one of its electrodes at a case potential andthis case is connected with a minus side of the semiconductor switchingcircuit. One unit of the second capacitor 12 is arranged to each of thesemiconductor switching circuit in each phase.

In this power conversion system in the fifth embodiment, each of thefirst capacitor 11a can be constructed in a small size by arranging twounits of the first capacitor 11a in parallel by each phase and itsinternal inductance also can be reduced and furthermore, the overallinductance of the capacitor portion can be reduced by arranging twounits in parallel with each other.

Further, as the cases of the first capacitors 11a are also used as minuselectrodes, it becomes possible not only to downsize the capacitors andmake inductance low but also to make an insulating distance with partsprovided around the first capacitors 11a less and to make the systemsmall in size and light in weight. Further, there is a merit from theviewpoint of safety if touched as the capacitors are normally at thesame potential as the earth potential as the cases become the minus sidepotential.

In addition, the connection to the first capacitors 11 from thesemiconductor devices 1 by conductors are two sets in parallel with eachother and thus, it becomes easy to reduce inductance of thesemiconductor switching circuit and a satisfactory switching operationis assured.

Sixth Embodiment

Next, the power conversion system in the sixth embodiment of the presentinvention will be described based on FIG. 8 and FIG. 9. FIG. 8 and FIG.9 show the construction of one set of semiconductor switching circuitsadopted in the power conversion system in the sixth embodiment.

The power conversion system in the sixth embodiment is an invertersystem and features in the construction wherein voltage drivinghigh-frequency switching devices capable of switching at above continual700 Hz like IGBT and IEGT, which are pressure fit semiconductor devicesare adopted for two series-connected semiconductor devices 1a comprisingthe semiconductor switching circuit and pressure fitted to thesemiconductor device cooler 5 and conductors 9f, 9g, 9h.

Two semiconductor devices 1a that are to be series connected arearranged in parallel with each other by facing the surface having smallinner thermal resistance to the cooler 5 and pressure fitted to thecooler 5 with an insulating plate 15 made of such material as aluminumnitride that is excellent in electric insulation and has large thermalconductivity put between them. Further, the capacitor 8 that serves as afilter capacitor as well as a surge voltage absorbing capacitor, thecooler 5 and the semiconductor devices 1a are arranged hierarchically,the negative pole of the upper arm side semiconductor device 1a and thepositive pole of the lower arm side semiconductor device 1a of eachsemiconductor switching circuit are electrically connected by theconductor 9f and the positive pole of the upper arm side semiconductordevice 1a and the negative pole of the lower arm side semiconductordevice 1a are electrically connected by one set of conductors 9g, 9hthat are closed to both ends of the capacitor 8, respectively. The closeone set of conductors 9g, 9h are electrically insulated by an insulator14 provided at their closed portion.

Further, as an inverter, one end of a conductor 10m is connected to theconductor 9f that is an intermediate connecting point of the upper andlower arm semiconductor devices 1a and AC power is output to a motor andfurther, conductors 10n, 10p are connected to both ends of the capacitor8 jointly with the conductors 9g, 9h in order to input DC power.Further, to compose a converter system, the conductor 10m is connectedto one phase of the AC input and DC power is taken from the conductors10n, 10p (This external connection is also applicable to the embodimentsshown below).

In the power conversion system of the sixth embodiment, at the portionswhere the conductors 9f, 9g, 9h interfere because of pressure of thepressure fit semiconductor devices 1a to the cooler 5 and the electricalconnection of the conductors 9f, 9g, 9h with the semiconductor devices1a, a hole 13 is provided on one conductor 9f so as to penetrate theconductor 9g as shown in FIG. 9 and these cooler 5, conductors 9f, 9g,9h and semiconductor devices 1a are fixed and electrically connected bystrongly clamping them simultaneously in the shape of sandwiches by apressing device (not shown) from the outside.

Thus, according to the power conversion system in the sixth embodiment,the semiconductor devices 1a are connected to the gate amplifier 6 bylead wires 17 and when a switching command is input, the semiconductordevices 1a make the switching operation. At this time, in order to makeinductance of the capacitor 8 and the semiconductor devices 1a as smallas possible, the capacitor 8 and the semiconductor devices 1a arebrought close to each other and the conductors 9f, 9g, 9h are also madeshort and closely arranged. Thus, inductance of the loop circuit couldbe suppressed to below 250 nH and in case of semiconductor devices ofrated voltage 3300V that are adopted in the main circuit for electricrailway car driving, a satisfactory switching characteristic can beobtained without causing the breaking by suppressing surge voltage Vp tobelow 3000V without a snubber circuit. As a result, a snubber circuit asa protective circuit around the semiconductor devices is eliminated andthe number of parts and kinds can be reduced sharply and also, in orderto eliminate a snubber resistor, thermal loss can be reduced and coupledwith reduction of the number of parts and kinds, simplifiedconfiguration, it is possible to achieve a small sized, light weightedand low priced system.

Further, in the sixth embodiment, the hole 13 is opened on the conductor9f and the interfering portion of the conductor 9g is penetrated throughthis hole. However, instead of this, it is possible to avoid theinterference with the conductor 9g by bending the interfering portion ofthe conductor 9f in the C-shape or notching it. Further, it is alsopossible to prevent the generation of the interference by shifting theconductor 9f laterally from the conductors 9g, 9h and the arrangementand shape of the conductors are not especially restricted.

Seventh Embodiment

Next, the power conversion system in the seventh embodiment of thepresent invention will be described based on FIG. 10. FIG. 10 shows theconstruction of one set of semiconductor switching circuits that areadopted in the power conversion system in the seventh embodiment. Thisseventh embodiment features that the same pressure fit semiconductordevices 1a as those in the sixth embodiment are adopted and thesemiconductor device cooler 5 is used as an intermediate connectingconductor of the upper and lower arm semiconductor devices.

In other words, two semiconductor devices 1a, that are to be seriesconnected and comprise the semiconductor switching circuit, are arrangedlaterally and opposing each other and the negative pole side of theupper arm side semiconductor device 1a and the positive pole side of thelower arm side semiconductor device 1a are press fitted to the sameplane of the cooler 5. Further, the filter capacitor 8 which also servesabsorbing the surge voltage, the cooler 5 and the semiconductor devices1a are arranged hierarchically, and the positive pole of the upper armside semiconductor device 1a and the negative pole of the lower arm sidesemiconductor device 1a are electrically connected to both terminals ofthe capacitor 8 by one set of closed conductors 9q, 9r. The sameinsulator 14 as that in the sixth embodiment is provided at the closeportion of this one set of conductors 9q, 9r for electrical insulation.

Further, a conductor (not shown) is connected to the cooler 5 at theintermediate connecting point of the upper and lower arm semiconductordevices 1a and is led out to the outside as the main circuit input point(in case of a converter circuit) or the main circuit output point (incase of an inverter circuit) and further, likewise the sixth embodiment,this conductor is connected together with the conductors 9q, 9r to bothterminals of the capacitor 8 and leads out to the outside as the maincircuit output point (In case of a converter circuit) or the maincircuit input point (in case of an inverter circuit).

In the power conversion system in this seven embodiment, because of thepressure of the press fitting semiconductor devices 1a to the cooler 5and the electrical connection of the conductors 9q, 9r to thesemiconductor devices 1a, the parts are fixed and electrically connectedby strongly clamping these cooler 5, conductors 9q, 9r and semiconductordevices 1a simultaneously from the outside by the pressing device (notshown) in the shape of sandwiches.

Thus, according to the power conversion system in the seventhembodiment, likewise the six embodiment, as the capacitor 8 and thesemiconductor devices 1a are brought close to each other, the cooler 5is used as an intermediate connecting conductor and the conductors 9q,9r are made short to bring them close to each other so as to minimizeinductance of the capacitor 8 and the semiconductor devices 1a as couldas possible, inductance of the loop shape circuit can be suppressed tobelow 250 nH and the same effect as that of the sixth embodiment isachieved.

Moreover, in case of this seventh embodiment, the number of conductorscan be reduced less than the sixth embodiment and the lengths also canbe made short, if this embodiment is adopted to the power conversionsystem that is used under the environment wherein no electric shockmeasure is especially required for the cooler 5, it becomes possible tofurther reduce the number of parts, simplify the construction and reduceprice.

Eighth Embodiment

Next, the power conversion system in the eight embodiment of the presentinvention will be described based on FIG. 11. FIG. 11 shows theconstruction of one set of semiconductor switching circuits that areadopted in the eighth embodiment. In the power conversion system in thiseighth embodiment, pressure fit semiconductor devices similar to thosein the sixth embodiment are adopted for two series-connectedsemiconductor devices 1a, and by facing the positive pole side of theupper arm side semiconductor device 1a and the negative pole side of thelower arm side semiconductor device 1a to the cooler 5, thesemiconductor devices 1a are press fitted to the cooler 5 by putting aninsulating plate 15 made of aluminum nitride that is excellent inelectric insulation and has a large thermal conductivity between them.Further, the capacitor 8 that serves as a filter capacitor and absorbssurge voltage, the cooler 5 and the semiconductor devices 1a arearranged hierarchically, the negative pole of the upper arm sidesemiconductor device 1a and the positive pole of the lower arm sidesemiconductor device 1a are electrically connected by a conductor 9s andthe positive pole of the upper arm side semiconductor device 1a and thenegative pole of the lower arm side semiconductor device 1a areelectrically connected to both terminals of the capacitor 8 by one setof conductors 9t, 9u that are close to each other. This one set ofconductors 9t, 9u is electrically insulated by providing the insulator14 at their close portion.

Further, a conductor (not shown) is connected to an intermediateconnecting point that is the conductor 9s connecting between the upperand lower arm semiconductor devices 1a and led out to the outside as themain circuit input point (in case of a converter circuit) or the maincircuit output point (in case of an inverter circuit) and further,likewise the sixth and seventh embodiments, a conductor is connectedjointly with the conductors 9t, 9u to both terminals of the capacitor 8and led out to the outside as the main circuit output point (in case ofa converter circuit) or the main circuit input point (in case of aninverter circuit).

Even in the power conversion system in this eighth embodiment, becauseof the pressure of the pressure fit semiconductor devices 1a to thecooler 5 and the electrical connection of the conductors 9s, 9t, 9u tothe semiconductor devices 1a, parts are fixed and electrically connectedby strongly clamping these cooler 5, conductors 9s, 9t, 9u andsemiconductor devices 1a in the shape of sandwiches simultaneously fromthe outside by a pressing device (not shown).

Thus, according to the power conversion system in the eighth embodiment,likewise the sixth and seventh embodiments, as the capacitor 8 and thesemiconductor devices 1a are brought to close each other and theconductors 9s, 9t, 9u are also made short in length to the mutuallyclosed shape and arrangement in order to minimize inductance of thecapacitor 8 and the semiconductors 1a as could as possible, inductanceof the loop shape circuit can be suppressed to below 250 nH and the sameeffect as that of the sixth embodiment is achieved.

Moreover, in case of this eighth embodiment, likewise the seventhembodiment, as the conductors can be made in a simple shape with lessbent portions and the length also can be made short, it becomes possibleto further reduce the number of parts, simplify the construction andreduce a price and further, as the cooler 5 is insulated, likewise thesixth embodiment, it is possible to expose at least the radiatingportion of the cooler to the outside, thus improving the cooling effect.

Further, in the power conversion system of this eighth embodiment,because of the pressure of the pressure fit semiconductor devices 1a andthe electrical connection of the conductors 9s, 9t, 9u to thesemiconductor devices 1a, likewise the construction shown in FIG. 9 asthe sixth embodiment, the hole 13 is provided on the conductor 9s at theportion where these conductors interfere to penetrate the conductors 9t,9u or the interfering portion of the conductor 9s is bent in the C-shapeor notched so as to avoid the interference with the conductors 9t, 9u.Further, it is also possible to prevent the generation of theinterference by shifting the conductor 9s laterally from the conductors9t, 9u and the arrangement and shape of the conductors are notespecially restricted.

Further, it is also possible to construct the power conversion system inthe eighth embodiment in such structure that two semiconductor devices1a that are to be connected in series in the eighth embodiment areturned over completely as in the seventh embodiment shown in FIG. 10, aninsulating plate that is excellent in insulation and has a large thermalconductivity like aluminum nitride is put between the cooler 5 and thesemiconductor devices 1a, the negative pole of the upper arm sidesemiconductor device 1a and the positive pole of the lower arm sidesemiconductor device 1a facing the cooler are connected by the conductor9s and the positive pole of the upper arm side semiconductor device 1aand the negative pole of the lower arm side semiconductor device 1a areconnected to both terminals of the capacitor 8 by the same conductor inthe seventh embodiment shown in FIG. 10. In this case, no interferenceis produced between the conductors and therefore, the shapes of theconductors in the eighth embodiment can be made simple and themanufacturing and assembling become easy.

Ninth Embodiment

Next, the power conversion system in the ninth embodiment will bedescribed based on FIG. 12 and FIG. 13. FIG. 12 shows the constructionof one set of semiconductor switching circuit that is adopted in thepower conversion system in the ninth embodiment and FIG. 13 shows theconstruction of an inverter circuit that is constructed by assembling 3sets of the semiconductor switching circuit in parallel. As shown inFIG. 12, the power conversion system in the ninth embodiment uses anearly rectangular shaped modular semiconductor device for thesemiconductor device 1b. This modular semiconductor device 1b is in suchstructure that positive and negative terminals are provided on onesurface and the other surface is a flat cooling and mounting surface formounting to the mounting board by bolts and nuts (not shown). Theelectrical characteristic of this modular semiconductor device 1b is thesame as that of the pressure fit semiconductor device adopted in theabove-mentioned embodiments and its operating characteristic is alsoequivalent to that of the pressure fit semiconductor device.

Two semiconductor devices 1b that are to be connected in series forconstructing semiconductor switching circuits are mounted on the sameplane of the semiconductor device cooler 5 close each other andlaterally so that the cooling and mounting surface is press fittedthereto. The upper and lower arm semiconductor devices 1b face in thesame direction, the positive terminal and negative terminals arepositioned at the upper and lower sides, respectively in FIG. 12, thenegative pole terminal of the upper arm side semiconductor device 1b andthe positive pole terminal of the lower side semiconductor device 1bwhich are near each other are electrically connected by a conductor 9vand further, the positive pole terminal of the upper arm sidesemiconductor device 1b and the negative pole terminal of the lower armside devices 1b are electrically connected to both terminal of thecapacitor 8 by one set of conductors 9w, 9x that are close to eachother. One set of these conductors 9w, 9x are electrically insulated byproviding the insulator 14 at their close portion.

3 sets of the semiconductor switching circuit thus assembled in theconstruction shown in FIG. 12 is provided in parallel as shown in FIG.13, U, V, W phase output conductors 10m for a three-phase AC motor areconnected to the conductors 9v of these switching circuits, DC inputconductors 10n, 10p are connected to both terminals of the capacitors 8of these 3 set of the switching circuits jointly with the conductors 9w,9x and an inverter circuit is composed by connecting these 3 sets of DCinput conductors 10n, 10p by common conductors 10q, 10r. Further, on thecontrary, it is possible to compose a converter circuit by connectingthe U, V, W phase input conductors to the conductors 9v of 3 sets of thesemiconductor switching circuits and using the conductors 10q, 10rcommonly connecting 3 sets of the conductors 10n, 10p as DC outputconductors.

In the power conversion system in this ninth embodiment, when thepositive pole P and the negative pole N of the DC input power source areconnected to the conductors 10q, 10r and the output conductor 10m isconnected to the U, V, W phase terminals of the 3-phase terminals of anAC motor, this power conversion system operates as an inverter circuitand drives the motor by converting DC power into 3-phase AC.

According to the power conversion system in the ninth embodiment in theabove-mentioned construction, likewise the sixth embodiment, as thecapacitor 8 and the semiconductor devices 1b are brought to close eachother and the length of conductors 9v, 9w, 9x are made short andarranged in order to minimize inductance of the capacitor 8 and thesemiconductor devices 1b as could as possible, inductance of the loopcircuit can be reduced to below 250 nH and in case of semiconductordevices of rated voltage 3300V that are adopted in a main circuit forelectric railway cars, good switching characteristic can be obtainedwithout breaking by voltage by suppressing surge voltage Vp to below3000V without a snubber circuit. As a result of the elimination of asnubber circuit as a protective circuit around semiconductor devices, itis possible to sharply reduce the number of parts and kinds and further,in order to eliminate a snubber resistor, reduce thermal loss andcoupled with reduction of number of parts and kinds and simplifiedconstruction, it becomes possible to realize a small sized, lightweighted and cheap price power conversion system.

In the ninth embodiment, as modular type semiconductor devices areadopted and the mounting surface sides of these devices are mounted tothe cooler, it is not needed to provide an insulating plate between thesemiconductor device and the cooler for insulation of the coolerlikewise pressure fit semiconductor devices and it becomes possible toreduce the number of parts on that point.

Further, in the ninth embodiment, the conductors 9w, 9x are bent toshift them from the conductor 9v laterally so as to avoid the interfere.However, a measure to avoid the interference is not restricted to thisand any one of measures enumerated in the explanation of the sixthembodiment can be adopted.

Tenth Embodiment

Next, the power conversion system in the tenth embodiment of the presentinvention will be described based on FIG. 14. FIG. 14 shows theconstruction of one set of semiconductor switching circuits adopted inthe tenth embodiment. The tenth embodiment features that the arrangementof modular type semiconductor devices 1b in the ninth embodiment shownin FIG. 12 is somewhat changed. That is, as shown in FIG. 14, the upperarm side semiconductor device 1b of two semiconductor devices 1b thatare to be connected in series and comprise the semiconductor switchingcircuit is so arranged that its positive pole terminal comes to the leftside and the negative pole terminal comes to the right side, and thelower arm side semiconductor device 1b is so arranged that its positivepole terminal comes to the right side and the negative pole terminalcomes to the left side, the negative pole terminal of the upper arm sidesemiconductor device 1b and the positive pole terminal of the lower armside semiconductor device 1b are electrically connected by a conductor9y and further, the positive pole terminal of the upper arm sidesemiconductor device 1b and the negative pole terminal of the lower armside semiconductor device 1b are electrically connected to bothterminals of the capacitor 8 by one set of close conductors 9z, 9aa.This one set of conductors 9z, 9aa is electrically insulated byproviding the insulator 14 to the near portion of these conductors.

It is possible to construct an inverter circuit when 3 sets of the thusassembled semiconductor switching circuit are arranged as shown in FIG.13 likewise the ninth embodiment, U-, V- and W-phase output conductorscorresponding to a 3-phase AC motor are connected to the conductors 9yof these switching circuits and a DC input conductor is connectedjointly with the conductors 9z, 9aa to both terminals of the capacitor 8of each of 3 sets of the semiconductor switching circuit. On thecontrary, it is possible to construct a converter circuit when the U-,V- and W-phase input conductors of 3-phase AC power source are connectedto the conductor 9y of the semiconductor switching circuit of each of 3sets and a DC output conductor is connected commonly to the conductors9z, 9aa of 3 sets of the semiconductor switching circuit.

The power conversion system in this tenth embodiment has the sameeffects as those in the ninth embodiment and it is possible to constructa power conversion portion without a snubber circuit, reduce the numberof parts and kinds, and achieve a small and light weighted system.

Eleventh Embodiment

Next, the power conversion system in the eleventh embodiment of thepresent invention will be described based on FIG. 15. The powerconversion system in the eleventh embodiment features that thesemiconductor device cooler is made a split structure. That is, twosemiconductor device coolers 5a are separately provided to cool each oftwo series-connected semiconductor devices 1a comprising thesemiconductor switching circuits as shown in FIG. 15. Other componentelements are the same as those in the sixth embodiment shown in FIG. 8and FIG. 9 and therefore, the detailed explanation of the constructionis omitted.

According to the power conversion system of this eleventh embodiment, asthe semiconductor device cooler 5a is provided to every semiconductordevice 1a, the temperature rise of a cooler by heat generation of one ofthe semiconductor does not affect the other cooler for cooling the othersemiconductor device and the efficient radiation becomes possible.

Further, the construction of the cooler 5a in the split structure isapplicable equally to any of the seventh through tenth embodiments forefficiently cooling the semiconductor devices 1a or 1b.

Twelfth Embodiment

Next, the power conversion system in the twelfth embodiment of thepresent invention will be describe based on FIG. 16. The twelfthembodiment features that not only the cooler is made in such structureas to cool each of the semiconductor devices 1a individually as in theeleventh embodiment shown in FIG. 15 but also the upper side cooler 5bfor the upper arm side semiconductor device 1a is provided with a largerradiation area than that of the lower side cooler 5c for the lower armside semiconductor device 1a in order to make the radiating area of acooler at the side where it is subject to heat radiated by a matingcooler and its temperature rises. Other component elements are the sameas those in the sixth embodiment shown in FIG. 8 and FIG. 9 and thedetailed explanation of the construction is omitted.

According to the power conversion system in this twelfth embodiment, asthe semiconductor device cooler is split into 5b and 5c for each of thesemiconductor devices 1a, the temperature rise of the cooler by the heatgeneration of the other semiconductor device does not affect the coolerfor cooling the other semiconductor device and the efficient radiationbecomes possible and furthermore, as the radiation area of the upperside cooler 5b that becomes the downstream side of the flow of heat ismade larger than that of the lower side cooler 5c, the drop of coolingefficiency of the upper side cooler 5b that is also subject to heat fromthe mating cooler 5c jointly with the semiconductor device 1a can besuppressed to the minimum.

Further, even in this twelfth embodiment, the construction of thesemiconductor device cooler split into the coolers 5b and 5c indifferent radiation areas is equally applicable to any of theabove-mentioned seventh through tenth embodiments in order toefficiently cool the semiconductor devices 1a or 1b.

Thirteenth Embodiment

Next, the power conversion system in the thirteenth embodiment of thepresent invention will be described based on FIG. 17. The powerconversion system in the thirteenth embodiment features that thesemiconductor device cooler is split into two units in differentradiation area shown by the reference numerals 5d, 5e and housed in anair duct 18. That is, the radiation area of the cooler 5d at thedownstream side position in the flow of cooling wind 19 flowing in theair duct 18 is made larger than that of the cooler 5e at the upperstream side position as shown in FIG. 17. Other component elements arethe same as those in the sixth embodiment shown in FIG. 8 and FIG. 9 andthe detailed explanation of the construction is omitted.

According to the power conversion system in this thirteenth embodiment,as the semiconductor device cooler is split into two units 5d and 5e foreach semiconductor device 1a, the temperature rise of the cooler by theheat generation of one semiconductor device does not affect the othercooler for cooling the other semiconductor device and the efficientradiation becomes possible and as the radiation area of the cooler 5d atthe downstream side position of the flow of the cooling wind 19 in theair duct 18 is made larger than that of the cooler 5e at the upperstream side position, the drop in cooling efficiency of the downstreamside cooler 5d subject to the heat from the mating cooler 5e jointlywith the semiconductor device 1a can be suppressed to the minimum.

Further, even in this thirteenth embodiment, the construction of thesemiconductor device cooler split into the coolers 5d and 5e indifferent radiation areas housed in the air duct 18 is equallyapplicable to any of the above-mentioned seventh through tenthembodiments in order to efficiently cool the semiconductor devices 1a or1b.

Fourteenth Embodiment

Next, the power conversion system in the fourteenth embodiment of thepresent invention will be described based on FIG. 18. The fourteenthembodiment features that a single unit of the cooler 5f is used for theupper and lower semiconductor devices 1a of each switching circuitwithout splitting it into two units and the mounting positions of theupper and lower semiconductor devices 1a against the cooler 5f areshifted to the upper stream side of the flow of heat (the lower side inFIG. 18) from the upper and lower symmetrical positions. Other componentelements are the same as those in the sixth embodiment shown in FIG. 8and FIG. 9 and the detailed explanation of the construction is omitted.

According to the power conversion system in this fourteenth embodiment,the semiconductor device 1a located at the downstream side of the flowof heat (the upper side in FIG. 18) is subject to the heat radiated fromthe radiating portion (not shown) of the cooler 5f and its coolingefficiency drops; however, when the mounting position of thesemiconductor device 1a located at the downstream side of the flow ofheat is shifted to the upper stream side of the flow of heat, theradiating area of the cooler corresponding to the semiconductor device1a located at the downstream side of the flow of heat becomes large andthe drop of cooling efficiency can be suppressed to the minimum.

Further, as in the fourteenth embodiment the construction wherein theradiating areas of one cooler 5f corresponding to the upper and lowersemiconductor devices 1a differ is equally applicable to any of theseventh tenth embodiments for efficiently cooling the semiconductors 1aor 1b.

Further, when the cooler 5f is housed in the air duct 18 as in thethirteenth embodiment shown in FIG. 17, it becomes possible toefficiently cool the semiconductor devices 1a similarly when themounting positions of the upper and lower semiconductor devices 1a areshifted to the windward side of a cooling wind 19.

Fifteenth Embodiment

The construction of the power conversion system in the fifteenthembodiment of the present invention will be described based on FIG. 19.This power conversion system adopted pressure fit semiconductor devices1a similar to those in the eleventh embodiment shown in FIG. 8 and FIG.9 and the cooler 5 that is in the thickness equal to these semiconductordevices 1a and equipped with a good conductive heat collecting blockportion 50 and a radiating portion 51 to radiate heat to the open air.For instance, if the cooler 5 is a heat pipe cooler to transport heat byutilizing phase change of refrigerant, this heat collecting blockportion 50 radiates heat by circulating refrigerant in the radiatingportion 51 utilizing a cooling block filled with refrigerant forboiling.

One set of semiconductor switching circuit that is adopted in the powerconversion system in this fifteenth embodiment adopts theabove-mentioned semiconductor devices 1a and the semiconductor cooler 5and by arranging two semiconductor devices 1a that are to be connectedwith the block portion 50 of the cooler 5 put between them and connectedin series using this block portion 50 as a conductor as shown in FIG.19.

That is, the negative pole side of the upper arm side semiconductordevice 1a is brought in contact with the top of the block portion 50 andthe positive pole side of the lower arm side semiconductor device 1a isbrought in contact with the bottom of the block portion 50 and further,the positive pole of the upper arm side semiconductor device 1a and thenegative pole of the lower arm side semiconductor device 1a areelectrically connected to both ends of the capacitor 8 by one set ofconductors 9ab, 9ac which are close to each other. These closeconductors are electrically insulated by providing the insulator 14 totheir close portion.

3 sets of thus assembled semiconductor switching circuit are provided inparallel with each other as shown in FIG. 13 likewise the ninthembodiment, the semiconductor devices 1a and the heat collecting blockportion 50 are press fitted by strongly clamping them from the upper andlower sides by a compressing device and by compressing the conductors9ab, 9ac and the semiconductor devices 1a, required portions areelectrically connected so as to effectively eliminate the heatgeneration of the semiconductor devices 1a by the cooler 5.

Then, U, V, W-phase output conductors for a 3-phase AC motor areconnected to the block portion 50 of the cooler 5 and DC inputconductors are connected jointly with the conductors 9ab, 9ac to bothends of each of 3 set capacitors 8, and an inverter circuit is thuscomposed. On the contrary, a converter circuit is composed by connectingthe U, V, W-phase input conductors for a 3-phase AC power source to theheat collecting block portion 50 that is an intermediate connectingpoint of each set of semiconductor switching circuit and by connecting aDC output conductor commonly to 3 sets of the conductors 9ab, 9ac.

In case of the fifteenth embodiment in the above-mentioned construction,as the block portion 50 of the cooler 5 also serves as a conductor toconnect between two semiconductor devices 1a connected in series in eachset of the semiconductor switching circuit, the conductor for connectingthe intermediate point of two semiconductor devices 1a (equivalent to,for instance, the conductor 9f shown in FIG. 8 and FIG. 9) becomesunnecessary and further, the overall areas of the electrode surfaces ofthe semiconductor devices 1a are connected in the shortest distance andinductance at this portion can be reduced remarkably. Further, as theterminals of the capacitor 8 are facing the semiconductor devices 1asides and two conductors 9ab, 9ac for connecting the semiconductordevices 1a and the capacitor 8 are close to each other, it is possibleto reduce inductance of this conductor portion and it becomes easy toreduce inductance of the loop circuit.

Therefore, according to the power conversion system in the fifteenthembodiment, it is possible to get the same effect as that in the ninthembodiment and construct a power conversion portion without a snubbercircuit and furthermore, because the system is in the structure that theheat collecting block portion 50 of the cooler 5 is clamped by the upperand lower semiconductor devices 1a, it is possible to reduce the numberof parts and kinds and to make the system in more small size and lightweight.

Further, if the terminals of the capacitor 8 are located at thepositions close to the heat collecting block portion 50 in thisfifteenth embodiment, the area enclosed by the loop circuit can be moresmall and inductance can be made more low.

Sixteenth Embodiment

Next, the power conversion system in the sixteenth embodiment of thepresent invention will be described based on FIG. 20. The sixteenthembodiment features that the heat collecting block portions 50 of thecooler 5 is compressed to the outsides of the upper and lowersemiconductor devices 1a in addition to the fifteenth embodiment shownin FIG. 19, one of the ends of the conductors 9ad, 9ae is connected tothese heat collecting block portions 50 and the other ends are broughtin close to each other and connected to both ends of the capacitor 8.

According to this sixteenth embodiment, it is possible to get the sameeffect as that of the fifteenth embodiment and further improve the heateliminating action as the upper and lower semiconductor devices 1a aresandwiched by the heat collection block portions 50 of the cooler 5 fromthe upper and lower sides.

Seventeenth Embodiment

Next, the power conversion system in the seventeenth embodiment of thepresent invention will be described based on FIG. 21. The seventeenthembodiment is applicable to a power conversion system that is used underconditions wherein it is expected that persons may touch the radiatingportion 51 of the cooler 5 requiring radiation by exposing it to theopen air and features the construction that the cooler 5 is electricallyinsulated from the semiconductor devices 1a.

The same semiconductor devices 1a and the cooler 5 as those in thefifteenth embodiment are adopted. Then, as shown in FIG. 21, twosemiconductor devices 1a that are to be connected in series are arrangedby facing the surfaces that their inner thermal resistances becomessmall (here, the positive pole side surfaces of the semiconductordevices 1a) to the front and back of the heat collecting block portions50 of the cooler 5 and press fitted to these block portions 50 via theinsulating plate 15 that is formed with a material excellent in electricinsulation and large thermal conductivity as aluminum nitride.

Then, the negative pole of the upper arm side semiconductor device 1aand the positive pole of the lower arm side semiconductor device 1a areconnected by the conductor 9af, while the positive pole of the upper armside semiconductor 1a and the negative pole of the lower arm sidesemiconductor device 1a are connected to both sides of the capacitor 8by one set of conductors 9ag, 9ah that are close each other. Theseconductors 9ag and 9ah are electrically insulated by the insulator 14provided at the portion near them.

3 sets of the thus assembled semiconductor switching circuit areprovided in parallel as shown in FIG. 13 likewise the fifteenthembodiment and by press fitting the semiconductor devices 1a and theheat collecting block portion 50 via the insulating plate 15simultaneously by strongly clamping them by the compressing device andfurther, required parts are electrically connected by press fitting theupper and lower semiconductor devices 1a and the conductors 9af, 9ag,9ah so that the heat generation of the semiconductor devices 1a can beeliminated effectively by the cooler 5.

Then, by connecting the U, V, W-phase output conductors of the 3-phaseAC motor to the conductor 9af of the block portion 50 of the cooler 5and DC input conductors to both ends of the capacitor 8 of each of 3sets jointly with the conductors 9ag, 9ah, an inverter circuit isconstructed. On the contrary, a converter circuit is constructed byconnecting the U, V, W-phase input conductors of the 3-phase AC powersource to the conductor 9af which is the intermediate connection of thesemiconductor switching circuit of each set and by connecting a DCoutput conductor commonly to the conductors 9ag, 9ah of each of 3 sets.

In case of the seventeenth embodiment in the above-mentionedconstruction, the same effect as that of the ninth embodiment isobtained and a power conversion portion can be constructed without asnubber circuit. In addition, as the heat collecting block portion 50 ofthe cooler 5 is clamped by the upper and lower semiconductor devices 1a,it is possible to reduce the number of parts and kinds and to realize asmall sized and light weighted system.

Further, in the nineteenth embodiment, if the terminals of the capacitor8 are located at the positions close and opposite to the heat collectingblock portion 5, the area enclosed by the looped circuit can be mademore small and inductance to the more low level.

Eighteenth Embodiment

Next, the power conversion system in the eighteenth embodiment of thepresent invention will be described in detail based on FIG. 22. Thepower conversion system in this eighteenth embodiment features that theheat collecting block portion 50 of the cooler 5 is also provided viathe insulating plate 15 to the outside of each of two series connectedupper and lower semiconductor devices 1a in the seventeenth embodimentshown in FIG. 21. Other constructions are common to those of theseventeenth embodiment.

According to this eighteenth embodiment, the semiconductor devices 1aare sandwiched by the heat collecting block portions 50 of the cooler 5likewise the sixteenth embodiment and in addition to the same effect asthat in the seventeenth embodiment, the semiconductor devices can beefficiently cooled.

Nineteenth Embodiment

Next, the power conversion system in the nineteenth embodiment of thepresent invention will be described based on FIG. 23. This nineteenthembodiment features that modular type semiconductor devices 1b similarto those in the ninth embodiment shown in FIG. 12 are adopted and thecooling and mounting surface sides of two semiconductor devices 1b thatare to be series connected for comprising one set of semiconductorswitching circuits against the cooler 5 comprising the heat collectingblock portion 50 and the radiating portion 51 are mounted back to backto the front and the back of the heat collecting block portion 50 sothat the negative pole terminal of the upper arm side semiconductordevice 1b and the positive pole terminal of the lower arm sidesemiconductor device 1b are at the positions opposite to each other.

Then, the negative pole terminal of the upper arm side semiconductordevice 1b and the positive pole terminal of the lower arm sidesemiconductor device 1b are connected by the conductor 9ai and further,the positive pole terminal of the upper arm side semiconductor device 1band the negative pole terminal of the lower arm side semiconductordevice 1b are connected to both terminals of the capacitor 8,respectively by the conductors 9aj, 9ak that are close to each other.

The power conversion system in this nineteenth embodiment constructs aninverter circuit or a converter circuit when 3 sets of the semiconductorswitching circuit shown in FIG. 23 are provided in parallel andconnected to an outside circuit likewise other embodiments.

According to the power conversion system in the nineteenth embodiment,likewise other embodiments, a power conversion system without a snubbercircuit can be constructed and in addition, by adopting modular typesemiconductor devices, even when their cooling and mounting surfacesides are brought in directly contact with the heat collecting blockportion 50 without an insulating plate, insulation of the cooler 5 canbe maintained and it becomes possible to construct a small and lightsystem accordingly.

Twentieth Embodiment

Next, the power conversion system in the twentieth embodiment will bedescribed based on FIG. 24. In the twentieth embodiment, module typesemiconductor devices 1b are adopted, two upper and lower semiconductordevices 1b to be connected in series for comprising a semiconductorswitching circuit are arranged at the positions so that their terminalsurfaces face each other and the negative pole terminal of one of thesemiconductor devices faces to the positive pole terminal of the othersemiconductor device, the heat collecting block portions 50 of thecoolers 5 are mounted to the cooling and mounting surfaces at theoutsides of both semiconductor devices 1b, the negative pole terminal ofthe upper arm side semiconductor device 1b and the positive poleterminal of the lower arm side semiconductor device 1b that are closeand facing each other are connected by a conductor 9am and further, thepositive pole terminal of the upper arm side semiconductor device 1b andthe negative pole side terminal of the lower arm are connected to bothterminals of the capacitor 8 by conductors 9an, 9ap that are close toeach other and thus, the semiconductor switching circuit is constructed.

In the power conversion system in this twentieth embodiment, likewiseother embodiment, an inverter circuit or a converter circuit isconstructed by providing 3 sets of the semiconductor switching circuitshown in FIG. 24 in parallel and connecting to an outer circuit.

According to the power conversion system in his twentieth embodiment,likewise other embodiments, there is an effect that a power conversionsystem without a snubber circuit can be constructed and in addition, byadopting modular type semiconductor devices, even when their cooling andmounting surface sides are brought in directly contact with the heatcollecting block portion 50 without an insulating plate, insulation ofthe cooler 5 can be maintained and it becomes possible to construct asmall and light system accordingly, and furthermore, it is possible toincrease the cooling effect by installing a separate cooler 5 to each ofthe semiconductor device 1b.

Further, if an interference is caused among the conductors in all theembodiments, the interference can be avoided by perforating a hole,bending or notching the portions causing the interference.

Further, in the sixth embodiment shown in FIG. 8 through the twentiethembodiment shown in FIG. 24, it is possible to make the construction touse the first capacitor 11 in the small capacity and low inductancesurge voltage absorbing instead of the capacitor 8 as shown in FIG. 3and FIG. 4 and connect the second capacitor 12 as a filter capacitor toit.

What is claimed is:
 1. A power conversion system characterized in thatcapacitors that serve as capacitors for filtering and absorbing surgevoltage are connected to both ends of series-connected semiconductordevices that are voltage driven high frequency switching devices inparallel, the connecting terminals of these capacitors are arranged sothat they are brought immediately close to the terminal positions of thesemiconductor devices, more than two sets of semiconductor switchingcircuits with inductance of which loop circuit comprising thesemiconductor devices and capacitors reduced to below 250 nH areconnected in parallel and both ends and an intermediate connecting pointof the series-connected semiconductor devices in each semiconductorswitching circuits are used as the main circuit terminals for externalconnection.
 2. A power conversion system according to claim 1,characterized in that the capacitors comprise more than two capacitorswith the same small capacity connected in parallel with each other.
 3. Apower conversion system according to claim 1 or 2, characterized in thatthe capacitors use their cases as the electrode terminal of either oneof the capacitors.
 4. A power conversion system according to claim 1,characterized in that the capacitors are arranged so that the electrodeterminals face the direction of the semiconductor devices.
 5. A powerconversion system according to claim 4, characterized in that theterminals of the capacitors are arranged immediately close to theintermediate position of the series-connected semiconductor devices. 6.A power conversion system according to claim 4, characterized in thatthe terminals of the capacitors are arranged immediately close to bothend positions of the series-connected semiconductor devices.
 7. A powerconversion system characterized in that the first capacitor for surgevoltage absorbing and the second capacitor as a filter capacitor withthe capacity larger than that of the first capacitor are connected toboth ends of the series-connected semiconductor devices that are voltagedriven high frequency switching devices, the first capacitor is arrangedat a position closer to the semiconductor devices than the secondcapacitor, more than two sets of semiconductor switching circuits withinductance of which loop circuit comprising the semiconductor devicesand the first capacitor is reduced to below 250 nH are connected inparallel, and both ends and intermediate connecting point of theseries-connected semiconductor devices in each semiconductor switchingcircuits are used as the main circuit terminals for the externalconnection.
 8. A power conversion system according to claim 7,characterized in that the first capacitor comprises more than twocapacitors with the same capacity connected in parallel.
 9. A powerconversion system according to claim 7 or 8, characterized in that thefirst capacitor uses the case as one of the electrode terminals of thefirst capacitor.
 10. A power conversion system according to claim 7,characterized in that the first capacitor is arranged so that itselectrode terminals face the direction of the semiconductor devices. 11.A power conversion system according to claim 10, characterized in thatthe terminals of the first capacitor are arranged immediately close tothe intermediate position of the series-connected semiconductor devices.12. A power conversion system according to claim 10, characterized inthat the terminals of the first capacitor are arranged immediately closeto both ends of the series-connected semiconductor devices.
 13. A powerconversion system according to claim 7, characterized in that thesemiconductor devices, first capacitor and second capacitor are arrangedhierarchically, the first capacitor is connected to both ends of theseries-connected semiconductor devices and the second capacitor isconnected to the connecting point, that is, the electrode terminal ofthe first capacitor.
 14. A power conversion system according to claim 7,characterized in that the number of units of the second capacitor isreduced to less than the number of sets of the semiconductor switchingcircuits that are connected in parallel and more than two sets of thesemiconductor switching circuits connected in parallel are connectedcommonly to at least one unit of the second capacitors.
 15. A powerconversion system according to claim 7, characterized in that the secondcapacitor is constructed as a filter capacitor with required capacity bya main capacitor in the main circuit unit including the semiconductordevices and auxiliary capacitor installed at the outside of the maincircuit unit.
 16. A power conversion system including more than two setsof semiconductor switching circuits connected in parallel comprisingsurge voltage absorbing capacitor connected in parallel to both ends ofseries-connected semiconductor devices that are voltage drivenhigh-frequency switching devices and both ends and the intermediateconnecting point of the series-connected semiconductor devices in thesemiconductor switching circuits are made the main circuit terminal forexternal connection, whereinthe semiconductor devices are press fitshape semiconductor devices of which both surfaces serve as theelectrode surfaces, the positive pole sides or the negative pole sidesof each semiconductor devices of an upper arm side and a lower arm sidein the series-connected semiconductor devices of the semiconductorswitching circuits are press fitted by way of an insulating plate havinglarge thermal conductivity on the same plane of semiconductor devicecooler, and the negative poles of the upper arm side semiconductordevices and the positive poles of the lower arm side semiconductordevices are connected by conductors and the positive poles of the upperarm side semiconductor devices and the negative poles of the lower armside semiconductor devices are connected by one set of conductors whichare close to both sides of the capacitors.
 17. A power conversion systemincluding more than two sets of semiconductor switching circuitsconnected in parallel comprising surge voltage absorbing capacitorsconnected in parallel to both ends of series-connected semiconductordevices that are voltage driven high-frequency switching devices andboth ends and the intermediate connecting point of the series-connectedsemiconductor devices in the semiconductor switching circuits are madethe main circuit terminal for external connection, whereinthesemiconductor devices are press fit shape semiconductor devices of whichboth surfaces serve as the electrode surfaces, the negative pole side ofthe upper arm side semiconductor device and the positive side of thelower arm side semiconductor device of the series-connectedsemiconductor devices of the semiconductor switching circuits are pressfitted on the same plane of the semiconductor device cooler of goodconductivity, and the positive pole of the upper arm side semiconductordevice and the negative pole of the lower arm side semiconductor deviceare connected respectively by one set of conductors that are close toboth terminals of the capacitors.
 18. A power conversion systemincluding more than two sets of semiconductor switching circuitsconnected in parallel comprising surge voltage absorbing capacitorsconnected in parallel to both ends of series-connected semiconductordevices that are voltage driven high-frequency switching devices andboth ends and the intermediate connecting point of the series-connectedsemiconductor devices in the semiconductor switching circuits as themain circuit terminals for external connection, whereinthe semiconductordevices are press fit shape semiconductor devices of which both surfacesserve as the electrode surfaces, the negative pole side of the upper armside semiconductor device and the positive pole side of the lower armside semiconductor devices of the series-connected semiconductor devicesof the semiconductor switching circuits are press fitted on the sameplane of the semiconductor device cooler with a common conductor putbetween them, and the positive pole of the upper arm side semiconductordevice and the negative pole of the lower arm side semiconductor deviceare connected respectively by one set of conductors that are close toboth terminals of the capacitors.
 19. A power conversion systemincluding more than two sets of semiconductor switching circuitsconnected in parallel comprising surge voltage absorbing capacitorsconnected in parallel to both ends of series-connected semiconductordevices that are voltage driven high-frequency switching devices andboth ends and the intermediate connecting point of the series-connectedsemiconductor devices in the semiconductor switching circuits as themain circuit terminals for external connection, whereinthe semiconductordevices are press fitted shape semiconductor devices of which bothsurfaces serve as the electrode surfaces, the positive pole sides of theupper arm side semiconductor devices and the negative pole sides of thelower arm side semiconductor devices of the series-connectedsemiconductor devices of the semiconductor switching circuits are pressfitted on the same plane of the semiconductor device cooler by way of aninsulating plate of large thermal conductivity, and the negative polesides of the upper arm side semiconductor devices and the positive polesides of the lower arm side semiconductor devices are connected byconductors, and the positive pole of the upper arm side semiconductordevice and the negative pole of the lower arm side semiconductor deviceare connected respectively by one set of conductors that are close toboth terminals of the capacitors.
 20. A power conversion systemincluding more than two sets of semiconductor switching circuitsconnected in parallel comprising surge voltage absorbing capacitorsconnected in parallel to both ends of series-connected semiconductordevices that are voltage driven high-frequency switching devices andboth ends and the intermediate connecting point of the series-connectedsemiconductor devices in the semiconductor switching circuits as themain circuit terminals for external connection, whereinthe semiconductordevices are modular type semiconductor devices provided with thepositive pole terminals and the negative pole terminals on one of thesurfaces and the opposite surfaces are flat cooling and mountingsurfaces, the series-connected semiconductor devices of thesemiconductor switching circuits are mounted on the same plane of thesemiconductor device coolers with the negative terminal sides of theupper arm side semiconductor devices and the positive pole sides of thelower arm side semiconductor devices arranged in parallel with andadjoining each other in the same directions, and the negative pole sidesof the upper arm side semiconductor devices and the positive pole sidesof the lower arm side semiconductor devices are connected by conductors,and the positive pole of the upper arm side semiconductor device and thenegative pole of the lower arm side semiconductor device are connectedrespectively by one set of conductors that are close to both terminalsof the capacitors.
 21. A power conversion system including more than twosets of semiconductor switching circuits connected in parallelcomprising surge voltage absorbing capacitors connected in parallel toboth ends of series-connected semiconductor devices that are voltagedriven high-frequency switching devices and both ends and theintermediate connecting point of the series-connected semiconductordevices in the semiconductor switching circuits as the main circuitterminals for external connection, whereinthe semiconductor devices aremodular type semiconductor devices provided with the positive poleterminals and the negative pole terminals on one of the surfaces and theopposite surfaces are flat cooling and mounting surfaces, theseries-connected semiconductor devices of the semiconductor switchingcircuits are mounted on the same plane of the semiconductor devicecoolers in the arrangement so that the line connecting the positive poleterminals and the negative pole terminals of the upper arm sidesemiconductor devices becomes in parallel with the line connecting thepositive pole terminal and the negative pole terminal of the lower sidearm semiconductor devices and the positive and negative directionsbecome opposite each other, and the negative pole sides of the upper armside semiconductor devices and the positive pole sides of the lower armside semiconductor devices are connected by conductors, and the positivepole of the upper arm side semiconductor device and the negative pole ofthe lower arm side semiconductor device are connected respectively byone set of conductors that are close to both terminals of thecapacitors.
 22. A power conversion system according to any one of claims16 through 21, characterized in that each of the semiconductor devicesis brought in contact with a separate semiconductor device cooler.
 23. Apower conversion system according to claim 22, characterized in that theradiation capacity of a semiconductor device cooler located at thedownstream side of the flow of air warmed by the radiation of thesemiconductor device cooler of the series-connected semiconductordevices is increased higher than that of the semiconductor device coolerlocated at the upper stream side.
 24. A power conversion systemaccording to any one of claims 16 through 21, characterized in that theseries-connected semiconductor devices are brought in contact with thesame semiconductor device cooler in the state where they are shifted tothe upper stream side of the flow of air warmed by the radiation of thesemiconductor device cooler.
 25. A power conversion system includingmore than two sets of semiconductor switching circuits connected inparallel comprising surge voltage absorbing capacitors connected inparallel to both ends of series-connected semiconductor devices that arevoltage driven high-frequency switching devices and both ends and theintermediate connecting point of the series-connected semiconductordevices in the semiconductor switching circuits as the main circuitterminals for external connection, whereinthe semiconductor devices arepress fit semiconductor devices of which both surfaces serve as theelectrode surfaces, the negative pole side of the upper arm sidesemiconductor device and the positive pole side of the lower arm sidesemiconductor device of the series-connected semiconductor devices ofthe semiconductor switching circuit are press fitted to the front andback of the heat collecting block portion of the semiconductor devicecooler having a flat and good conductive heat collecting block portionand a radiating portion to radiate the heat collected by this heatcollecting block portion, respectively, the positive pole of the upperarm side semiconductor device and the negative pole of the lower armside semiconductor device are connected by one set of conductors thatare close to both terminals of the capacitor, respectively.
 26. A powerconversion system including more than two sets of semiconductorswitching circuits connected in parallel comprising surge voltageabsorbing capacitors connected in parallel to both ends ofseries-connected semiconductor devices that are voltage drivenhigh-frequency switching devices and both ends and the intermediateconnecting point of the series-connected semiconductor devices in thesemiconductor switching circuits as the main circuit terminals forexternal connection, whereinthe semiconductor devices are press fitsemiconductor devices of which both surfaces serve as the electrodesurfaces, the negative pole side of the upper arm side semiconductordevice and the positive pole side of the lower arm side semiconductordevice of the series-connected semiconductor devices of thesemiconductor switching circuit are press fitted to the front and backof the heat collecting block portion of the semiconductor device coolerhaving a flat and good conductive heat collecting block portion and aradiating portion o radiate the heat collected by this heat collectingblock portion, respectively, the heat collecting block portions ofseparate two semiconductor device coolers that have flat good conductiveheat collecting block portions and radiating portions to radiate theheat collected by this heat collecting block portions are press fit tothe positive pole side of the upper arm side semiconductor device andthe negative pole side of the lower arm side semiconductor device,respectively, and the heat collecting block portion of the separatesemiconductor device cooler to which the positive pole side of the upperarm side semiconductor device is press fitted and the heat collectingbock portion of the separate semiconductor device cooler to which thenegative pole side of the lower arm side semiconductor device is pressfitted are connected to both terminals of the capacitor by one set ofconductors that are close to each other.
 27. A power conversion systemincluding more than two sets of semiconductor switching circuitsconnected in parallel comprising surge voltage absorbing capacitorsconnected in parallel to both ends of series-connected semiconductordevices that are voltage driven high-frequency switching devices andboth ends and the intermediate connecting point of the series-connectedsemiconductor devices in the semiconductor switching circuits as themain circuit terminals for external connection, whereinthe semiconductordevices are press fit semiconductor devices of which both surfaces serveas the electrode surfaces, the same positive pole surface sides or thenegative pole surface sides of the series-connected semiconductordevices of the semiconductor switching circuits are press fitted to thefront and back of the heat collecting block portion of the semiconductordevice cooler having the flat heat collecting block portion and theradiating portion to radiate the heat collected by this heat collectingblock portion by way of electric insulating plate having large thermalconductivity, respectively, the negative pole side of the upper arm sidesemiconductor device and the positive pole side of the lower arm sidesemiconductor device of the series-connected semiconductor devices areconnected by conductors, and the positive pole of the upper arm sidesemiconductor device and the negative pole of the lower arm sidesemiconductor device are connected to both terminals of the capacitor byone set of conductors that are close to each other.
 28. A powerconversion system including more than two sets of semiconductorswitching circuits connected in parallel comprising surge voltageabsorbing capacitors connected in parallel to both ends ofseries-connected semiconductor devices that are voltage drivenhigh-frequency switching devices and both ends and the intermediateconnecting point of the series-connected semiconductor devices in thesemiconductor switching circuits as the main circuit terminals forexternal connection, whereinthe semiconductor devices are press fitsemiconductor devices of which both surfaces serve as the electrodesurfaces, the same positive pole surface sides or the negative polesurface sides of the series-connected semiconductor devices of thesemiconductor switching circuits are press fitted to the front and backof the heat collecting block portion of the semiconductor device coolerhaving the flat heat collecting block portion and the radiating portionto radiate the heat collected by this heat collecting block portion byway of electric insulating plate having large thermal conductivity, theheat collecting block portions of separate two semiconductor devicecoolers that have flat heat collecting block portions and radiatingportions to radiate the heat collected by this heat collecting blockportions are press fit to the electrode surface positioned at theoutside of the upper arm side semiconductor device and the electrodeside positioned at the outside of the lower arm side semiconductordevice, respectively by way of an insulating plate having large thermalconductivity, the negative pole side of the upper arm side semiconductordevice and the positive pole side of the lower arm side semiconductordevice of the series-connected semiconductor devices are connected byconductor, and the positive pole of the upper arm side semiconductordevice and the negative pole of the lower arm side semiconductor deviceare connected to both terminals of the capacitor by one set ofconductors that are close to each other.
 29. A power conversion systemincluding more than two sets of semiconductor switching circuitsconnected in parallel comprising surge voltage absorbing capacitorsconnected in parallel to both ends of series-connected semiconductordevices that are voltage driven high-frequency switching devices andboth ends and the intermediate connecting point of the series-connectedsemiconductor devices in the semiconductor switching circuits as themain circuit terminals for external connection, whereinthe semiconductordevice is modular type semiconductor device provided with the positiveand negative terminals on one of its surfaces and the opposite surfaceis a flat cooling and mounting surface, the series-connectedsemiconductor devices of the semiconductor switching circuits are soarranged that the mount surfaces face each other and the negative poleterminal of one of the semiconductor devices is positioned on the backside of the positive pole terminal of the other semiconductor device,the mounting surface sides of the series-connected semiconductor devicesof the semiconductor switching circuits are mounted on the front andback sides of the heat collecting block portions of the semiconductordevice cooler that has a flat heat collecting block portion and aradiating portion to radiate the heat collected by this heat collectingblock portion, respectively, the negative pole terminal of the upper armside semiconductor device and the positive pole terminal of the lowerarm side semiconductor device of the series-connected semiconductordevices are connected by a conductor, and the positive pole terminal ofthe upper arm side semiconductor device and the negative pole terminalof the lower arm side semiconductor device are connected to bothterminals of the capacitor by one set of conductors that are close toeach other.
 30. A power conversion system including more than two setsof semiconductor switching circuits connected in parallel comprisingsurge voltage absorbing capacitors connected in parallel to both ends ofseries-connected semiconductor devices that are voltage drivenhigh-frequency switching devices and both ends and the intermediateconnecting point of the series-connected semiconductor devices in thesemiconductor switching circuits as the main circuit terminals forexternal connection, whereinthe semiconductor device is a modular typesemiconductor device provided with the positive and negative terminalson one of its surfaces and the opposite surface is a flat cooling andmounting surface, the series-connected semiconductor devices of thesemiconductor switching circuits are so arranged that the mountingsurfaces come to the outside and the positive pole terminal and negativepole terminal face each other, the heat collecting block portions ofsemiconductor device coolers that have a flat heat collecting blockportion and a radiating portion to radiate the heat collected by thisheat collecting block portion are mounted on the mounting surfaces ofthe series-connected semiconductor devices, the negative pole terminalof the upper arm side semiconductor device and the positive poleterminal of the lower arm side semiconductor device of theseries-connected semiconductor devices are connected by a conductor, andthe positive pole terminal of the upper arm side semiconductor deviceand the negative pole terminal of the lower arm side semiconductordevice are connected to both terminal of the capacitor, respectively byone set of conductors that are close to each other.
 31. A powerconversion system according to claim 16, characterized in that thecapacitor is one capacitor that serves as a filter capacitor and forsurge voltage absorbing.
 32. A power conversion system according toclaim 16, characterized in that the capacitor is the first capacitor outof the first capacitor for surge voltage absorbing and the secondcapacitor as a filter capacitor.